a character string naming an algorithm to compute the
number of cells (see ‘Details’),

a function to compute the number of cells.

In the last three cases the number is a suggestion only; the
breakpoints will be set to pretty values. If
breaks is a function, the x vector is supplied to it
as the only argument.

freq

logical; if TRUE, the histogram graphic is a
representation of frequencies, the counts component of
the result; if FALSE, probability densities, component
density, are plotted (so that the histogram has a total area
of one). Defaults to TRUEif and only ifbreaks are
equidistant (and probability is not specified).

probability

an alias for !freq, for S compatibility.

include.lowest

logical; if TRUE, an x[i] equal to
the breaks value will be included in the first (or last, for
right = FALSE) bar. This will be ignored (with a warning)
unless breaks is a vector.

the density of shading lines, in lines per inch.
The default value of NULL means that no shading lines
are drawn. Non-positive values of density also inhibit the
drawing of shading lines.

angle

the slope of shading lines, given as an angle in
degrees (counter-clockwise).

col

a colour to be used to fill the bars.
The default of NULL yields unfilled bars.

border

the color of the border around the bars. The default
is to use the standard foreground color.

main, xlab, ylab

these arguments to title have useful
defaults here.

xlim, ylim

the range of x and y values with sensible defaults.
Note that xlim is not used to define the histogram (breaks),
but only for plotting (when plot = TRUE).

axes

logical. If TRUE (default), axes are draw if the
plot is drawn.

plot

logical. If TRUE (default), a histogram is
plotted, otherwise a list of breaks and counts is returned. In the
latter case, a warning is used if (typically graphical) arguments
are specified that only apply to the plot = TRUE case.

labels

logical or character string. Additionally draw labels on top
of bars, if not FALSE; see plot.histogram.

nclass

numeric (integer). For S(-PLUS) compatibility only,
nclass is equivalent to breaks for a scalar or
character argument.

warn.unused

logical. If plot = FALSE and
warn.unused = TRUE, a warning will be issued when graphical
parameters are passed to hist.default().

Details

The definition of histogram differs by source (with
country-specific biases). R's default with equi-spaced breaks (also
the default) is to plot the counts in the cells defined by
breaks. Thus the height of a rectangle is proportional to
the number of points falling into the cell, as is the area
provided the breaks are equally-spaced.

The default with non-equi-spaced breaks is to give
a plot of area one, in which the area of the rectangles is the
fraction of the data points falling in the cells.

If right = TRUE (default), the histogram cells are intervals
of the form (a, b], i.e., they include their right-hand endpoint,
but not their left one, with the exception of the first cell when
include.lowest is TRUE.

For right = FALSE, the intervals are of the form [a, b),
and include.lowest means ‘include highest’.

A numerical tolerance of 1e-7 times the median bin size
(for more than four bins, otherwise the median is substituted) is
applied when counting entries on the edges of bins. This is not
included in the reported breaks nor in the calculation of
density.

The default for breaks is "Sturges": see
nclass.Sturges. Other names for which algorithms
are supplied are "Scott" and "FD" /
"Freedman-Diaconis" (with corresponding functions
nclass.scott and nclass.FD).
Case is ignored and partial matching is used.
Alternatively, a function can be supplied which
will compute the intended number of breaks or the actual breakpoints
as a function of x.

Value

an object of class "histogram" which is a list with components:

breaks

the n+1 cell boundaries (= breaks if that
was a vector). These are the nominal breaks, not with the boundary fuzz.

counts

n integers; for each cell, the number of
x[] inside.

density

values f^(x[i]), as estimated
density values. If all(diff(breaks) == 1), they are the
relative frequencies counts/n and in general satisfy
sum[i; f^(x[i])
(b[i+1]-b[i])] = 1, where b[i] = breaks[i].